1. Field of the Invention
The present invention relates to an improved process for the conversion of an aromatic hydrocarbon in the presence of a titanium tetrafluoride catalyst system. The invention will be described with reference to alkylation, e.g., the synthesis of cumene by alkylation of benzene with propylene in the presence of the catalyst. The invention may also be used for alkylaromatic transalkylation and isomerization.
2. Description of the Prior Art
Conversion of aromatic hydrocarbons is well known in industry. Some of the aromatic conversion reactions which occur include alkylation of aromatic hydrocarbons with an alkylating agent such as an olefin, disproportionation or transalkylation of alkylaromatic hydrocarbons and isomerization of alkylaromatic hydrocarbons such as xylenes, and of dialkyl and higher substituted aromatics.
Of special interest, has been the propylation of benzene to cumene. Cumene is used for the production of phenol and acetone. Cumene is also dehydrogenated to form methylstyrene, in a process similar to that used to convert ethylbenzene to styrene. Cumene is also used as a blending component in aviation gasoline because of its high octane number. The consumption of cumene in the U.S.A. was about 350,000 metric tons in 1968. Of this total, 94% was used for the production of phenol or acetone.
It is well known that cumene can be synthesized from benzene and propylene using a catalyst of AlCl.sub.3, SPA or BF.sub.3. SPA is a generally accepted abbreviation for solid phosphoric acid catalyst, or phosphoric acid which is adsorbed on kieselguhr or other support.
AlCl.sub.3 is a very popular alkylation catalyst, because of its high activity. Unfortunately, the catalyst operates as a slurry or sludge which is messy to handle on a commercial scale, and also is corrosive. The highly reactive nature of this Friedel-Crafts metal halide catalyst, AlCl.sub.3, is desirable when attempting to alkylate benzene with ethylene, because less active catalyst systems do not work. However, for alkylation with propylene such highly reactive systems are not necessary.
Another highly selective catalyst system has been developed for the alkylation of benzene with olefins. This catalyst comprises boron trifluoride. The boron trifluoride catalyst system is exceptionally active and permits operation with dilute olefin streams, but it requires the continuous addition of BF.sub.3 to maintain catalyst activity. High catalyst activity also leads to oligomerization of olefins so contact time of olefins with BF.sub.3 catalyst should be as short as possible. This catalyst is also exceptionally water sensitive, as water not only destroys the catalyst, but produces very corrosive solutions which attack downstream processing units. BF.sub.3 also frequently appears in the product and must be removed therefrom.
Because of the interest in alkylating benzene with propylene to make cumene, and because of the inadequacies of existing catalyst systems, I studied the work that others had done, and made exhaustive investigations to determine if it would be possible to find a catalyst which would have the activity and selectivity required to produce an acceptable cumene product, while making maximum use of existing petroleum resources and provide an improved process for the manufacture of cumene.
A highly active catalyst was sought to operate with less catalyst and to reduce operating or construction cost. In new units this would mean smaller, and cheaper reactor vessels, while in existing units it would mean that an increase in capacity could be obtained merely by changing catalyst in an existing reactor vessel with only minor modifications of the plant.
High selectivity is necessary, not only to permit operation with feedstreams which are not 100% pure propylene, but also to maximize production of the desired cumene product, and to minimize production of polymerized olefins, or polyalkylated aromatic compounds.
Accordingly, many catalyst systems were studied to find a catalyst with excellent activity and selectivity, which was not corrosive or destroyed by water.
There has been extensive work done with Ti catalysts, thought most work occurred in conjunction with studies of Ziegler-Natta catalysts. The closest prior art known is U.S. Pat. Nos. 2,381,481 (Class 260-683.15), 2,951,885 (Class 260-671), 2,965,686 (Class 260-671) and 3,153,634 (Class 252-429).
In U.S. Pat. No. 2,381,481, preparation and use of a catalyst prepared by treating alumina gel with fluotitanic acid is disclosed. This catalyst is used for polymerization of olefins to heavier hydrocarbons, and also for alkylation of paraffins with olefins, the latter when operating at high temperatures, between 700.degree. and 900.degree. F. or higher. No mention is made of alkylation of aromatics with olefinic hydrocarbons.
In U.S. Pat. No. 2,951,885, there is disclosed the use of titanium trihalide on activated alumina or other activated acidic oxide for alkylation of benzene with olefins. The catalyst is originally a tetrachloride, subsequently reduced to the trichloride with an alkali metal such as sodium, lithium, or potassium. The examples show that this catalyst will alkylate benzene with ethylene.
In U.S. Pat. No. 2,965,686, the thrust of the application was to develop a titanium subchloride catalyst. In Example II, a reaction between cumene and propylene was disclosed using titanium tetrachloride catalyst. The catalyst in Example II was not a subfluoride, but rather was a tetrachloride. The reaction occurred for almost three hours at 146.degree. C. in a vessel containing 43 grams of catalyst and 128 grams of cumene. Almost 64% of the cumene was not reacted, while the isopropyl cumene yield was 27.3%, and 2.6% yield of heavier material. It is not certain if the results obtained in this patent are due solely to the use of the tetrachloride, as opposed to the tetrafluoride of applicant's process, or whether the method of preparation of applicant's tetrafluoride also makes a contribution to the improved activity of applicant's catalyst.
In U.S. Pat. No. 3,153,634, there is disclosed the use of titanium subhalides in a polymerization reaction. The patentee is probably describing a form of catalyst to make high molecular weight polymer, as he discusses production of solid polymer products. The patentee in 3,153,634 taught the very antithesis of applicant's reaction. Thus, on page 3 line 65-75, the patentee mentions use of benzene as an inert solvent to hold dissolved olefins, rather than as a reactant.
Accordingly, work continued on developing an improved process for the catalytic conversion of aromatic hydrocarbons.
Accordingly, the present invention provides a process for the catalytic conversion of an aromatic hydrocarbon comprising contacting the aromatic hydrocarbon with a reactant in the presence of a catalyst comprising titanium tetrafluoride composited with a support which contains surface hydroxyl groups and recovering a converted aromatic hydrocarbon as a product of the process.